PROJECT SUMMARY Clefting of the secondary palate is one of the most common congenital anomalies, with a prevalence of 1/1,500 live births. Individuals with cleft palate can be treated by a team of specialists to functional and esthetic norms; however, the current treatment requires multiple surgeries throughout life, which are associated with significant morbidities, and thus, there is an opportunity to improve therapies and outcomes. An increased understanding of the biological processes underlying palatogenesis will provide a foundation on which improved interventions and therapies will be built for patients with cleft palate. Secondary palate development is a complex, multi-step process in which the palatal shelves develop from the maxillary processes and grow vertically, lateral to the developing tongue. The palatal shelves then reorient into a horizontal position dorsal to the tongue in a process termed palatal shelf elevation. The shelves grow horizontally to meet at the midline and fuse to form the hard and soft palate that separate the oral and nasal cavities. The process of palatal shelf elevation is one of the least understood aspects of palatogenesis. Tremendous change in tissue tension and morphology occurs in the palatal shelves during palatal shelf elevation, yet how tension is generated and interpreted by the cells to result in tissue remodeling is not understood. The Hippo pathway is a recently discovered mechanosensory pathway that regulates organ size and tissue repair by controlling proliferation, apoptosis, and differentiation. The downstream targets of the Hippo pathway, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), translocate to the nucleus and regulate gene transcription in response to change in cell geometry, extracellular matrix (ECM) stiffening, and physical stretching. In order to probe for a link between tension and morphological change in the palatal shelves during elevation, this proposal investigates the Hippo signaling pathway in secondary palate formation. Deletion of Yap and Taz in a subset of secondary palate mesenchymal cells results in cleft palate and, specifically, defects in palatal shelf elevation. This research proposal will determine the role of YAP/TAZ in palatal shelf elevation and test the hypothesis that YAP/TAZ are activated by tension in the palatal shelves, created by ECM and cytoskeleton remodeling, to induce gene transcription required for elevation. Aim 1 will analyze changes in the palatal mesenchyme with deletion of Yap and Taz and determine the role of Hippo signaling in palatogenesis. Aim 2 will establish the molecular mechanism of action of YAP/TAZ in palate development by determining transcriptional targets of YAP/TAZ. This work will bring new insight into the physical and cellular biology underlying palate elevation that will broaden our understanding of palatogenesis and clefting of the secondary palate, guiding future therapies for patients with cleft palate.